Crystal mounting and circuit arrangement



Sept. 1, 1931. J. R. HARRISON CRYSTAL MOUNTING AND CIRCUIT ARRANGEMENT Filed Jan. 4, 1929 3S heets-Sheet 1 I INVENTOR. MJ ww 3L, 3PM:

ATTORNEYS ept. 1, 1931. J. R. HARRISON 7 1,821,304

CRYSTAL MOUNTING AND CIRCUIT ARRANGEMENT Filed Jan. 4. 1929 3 Sheets-Sheet 2 I INVEiY TOR. Jami/90M 3, MW,

BY A d QiTTORNEY}.

Sept, 1, 1931. J. R. HARRISON CRYSTAL MOUNTING AND CIRCUIT ARRANGEMENT Filed Jan. 4, 1929 5 Sheets-Sheet 5 INVENTOR. Jami 00w 5L Maw,

BY 5 ATTOR EYI.

Patented Sept. 1, 1931 UNITED STATESfPATENT OFFICE JAMISON HARRISON, OF MIDDLETOWN, CONNECTICUT, ASSIGNORiTOWIRED RADIO, ENG, OF NEW YORK, N. Y., A CORPORATION OF DELAWARE I CRYSTAL MOUNTING AND CIRCUIT ARRANGEMENT My invention relates broadly to crystal mountings and circuit arrangements employed in high frequency Signaling systems.

An object of my invention is to provide a mounting for piezo electric crystals for exciting fiexural vibrations.

Another object of my invention is to provide a crystal mounting adapted to be emplosyed with a screen grid thermionic tube.

till another object of my invention is to provide a crystal mounting adapted to be euiployed with a screen grid thermionic tube and an improved circuit arrangement. a

A further object of my invention is to provide a piezo electric crystal mounting and electron tube circuit therefor wherein oscillations are sustained by energy feed back through the crystal.

The embodiments. of my invention can best be understood by referring to the specification following and to the accompanying drawings which are a schematic circuit diagram and a perspective view of the crystal mounting of my invention.

It is very desirable to use the screen grid tube in circuit arrangements for producing flexural vibrations because of the large power output obtainable and the comparative ease with which crystal controlled oscillations are obtained. In one method of thus using the screen grid tube, a large direct current electrostatic potential is applied to one edge of the crystal and between the cathode and anode of the tube, and another potential of lower value is applied across the other long edge of the crystal and betweenthe control gridand cathode. .That is, ordinarily when using the conventional crystal mounting for flexural vibrations with the type of circuit here described, one pair of electrodes, for example those-alon the lower edge of the crystal, are connecte to the input of the ampli- 'fier, and those along the upper edge would be connected to the output of the amplifier. The earlier conventional mountings of this type with associated circuits have been described by J. R. Harrison in the Proceedings of the Institute of Radio Engineers, vol. 15, pages 1040-1054 December, 1927; and

vol. 16, page'1455, ovember, 1928, and by Giebe and Scheibe, Zeitschrift fiir Physik, vol. 46, page 607, J anuary 25, 1928. Since the electromotive force in t e input of the amplifier is much smaller than the output electromotive force, the electromotive force applied to the lower edge of the crystal would be much smaller than that applied to the upper edge. But the strain set up in the piezo electric crystal is proportional to the applied electromotive force so that the strain along the lower edge of the crystal is much smaller than that along the upper edge. Therefore, this method causes the strain in the crystal plate, due to the applied electrostatic field, to be unsymmetrical. The unsymmetry is an undesirable characteristic and is to be avoided for best results. One undesirable result may be fracture of the crystal. It is an object of my invention to provide a method of avoiding this undesirable condition.

The crystal mounting and circuit arrangement of my invention provides an improved method for exciting fiexural vibrations of the crystal as well as other types of vibration. This mounting when properly designed increases the power output obtainable from a given crystal plate and applies the electric field in a more symmetrical manner so that the resultant strain in the plate is more uniform. With a more uniform strain the denger of breaking the crystal plate is very much reduced. This new mountin is especially adapted to piezo electric oscillator circuits using feedback through the crystal itself. The nature and purpose of my invention may be most readily comprehended by reference to the appended drawings. Figs. 1 and 2 show\one embodiment of the crystal mount ing of my invention and two kinds of circuits suitable for use therewith. Figures 3, 4' and 5 show diagrammatically a piezo electric crystal with various arrangements of electrodes and related circuits from which the operation of the system of my invention will be better understood. Referring to Fig.

1, mounting in its entirety comprises six elecof the earlier method of mounting which I have referred to above. Electrodes 1, and 3 are equal in length and electrode 2 ma be either longer, shorter or equal in length to electrodes 1 and 3 dependin upon the size of the crystal and the electrlcal circuit employed. An oscillator circuit employing the crystal mounting of my invention, wherein a screen grid tube is employed, is illustrated in the accompanying drawings. Electrode 2 of the crystal mounting is connected to the control grid 7 of thermionic tube 20. Elec-- trodes 1, 3 and 5 are electrically connected by wires and connected to anode 10. Elec-' green grid 9 is supplied with a positive potential bias in respect to cathode 8. A battery 13 is herein shown as a source of anode potential, however any suitable source can be used. Cathode 8 is energized by source 15. The proper potential bias is impressed upon control grid 7 from source 16 through choke '17. Choke 17 is designed to exclude the oscillatory currents from source 16. In the crystalmounting of my invention the electrodes 1, 2, 3, 4, 5 and 6 may be separated and properly spaced with respect to crystal X by spacers of insulatin material. Electrodes 1, 2, 3, 4, 5 and 6 an the suitable'insulating spacers are held in place by machine screws,

,pins or other convenient means so that the whole system is rigid. The mounting in its entirety may be enclosed in a hermetically sealed container in which may be placed a thermostat to control the temperature within desired limits.

The particular circuit arrangement shown in Fig. 1 is not the only circuit that may be employed with my mounting and it is sometimes desirable to connect the electrodes in another manner and still maintain the desired symmetry. As an example, in another form of circuit shown in Fig. 2, electrodes 1 and 3 are joined together and connected to control grid 7. Electrodes 2 and 5 are joined together and connectedto anode 10. The electrodes 4 and 6 are joined together and'connected to the filament as shown in Fig. 2. p n the arrangement shown in Fig. 2, the

cuit is applied between electrodes 1 and 3,

and electrodes 4 and 6. The high otential from the output is therefore applie to both edges of the crystal and the strains set up in the crystal plate by the electric fields are more uniform, and there is less danger of breaking the crystal plate. The distribution of the electric fields using the arrangement of Fig. 2 is therefore also more s mmetrical than 111 the ordinary mounting or flexural vibrations heretofore known, and the arrangement of Fig. 2 has distinct advantages over the arrangements heretofore known. In the particular applications in which I have employed the mountings shown in Figs. 1 and 2, I have usually found the arrangement ofFig. 1 to give better results than the arrangement of Fig. 2, but under some circumstances the arrangement of Fig. 2 will have advantages. In the new type of mountings which I have here described, the output voltage of the tube is applied to both edges of the crystal sothat the strain along both edges .is the same, and the strains "are consequently much more uniform. The particular construction which I have described is necessary because the output voltage cannot applied along the entire length of both edges of the crystal, since electrodes must be provided for the input electromotive force from the crystal to the tube. For this're'ason one of the electrodes is divided into three parts, 1, 2 and 3 (Figs. 1 and 2). Two of these electrodes, 1 and 3, are connected together and serve as one of the connections to the output of the tube, while the third electrode 2, serves as the connection to the input (Fig. 1), or these connections are interchanged as shown in Fig. 2. With either arrangement, the output electromotive force is supplied to both edges of the crystal. The electrode must be divided into three arts in order to obtain this symmetry. Ot er methods of connecting the electrodes together for maintaining symmetry of the system may also be em-.

ployed. Although the mounting herein de-' scribed is used for exciting flexural vibrations in the length-breadth plane of the crystal plate, it is obvious that this manner of design is not limited only to the production of these particular flexural vibrations. When flexural vibrations are excited by the crystal mounting of my invention,there may be obtained flexural vibrations in the lengthbreadth plane of a quartz plate cut in the conventional or Curie-cut manner. Besides the vibrations which have been described, as is Well known, flexural vibrations can be excited in other planes in this type of crystal 'plate and also in plates'cut in different orientations by exciting the crystal with plates applied in the proper planes and the proper manner. In these cases also it is further possible to split. up the original electrodes of the crystal mounting and apply the electric -nected to the plate, and E to the grid.

field in a symmetrical manner. Circuits employing energy feed back through the piezo electric crystal are at present generally employed at frequencies below 100,000 cycles per second. Since vibrations of these lower frequencies are very often of the. flexural type, in describing a specific embodiment of my invention I have referred to vibrations of'the fiexural type but, I do not in any way intend to limit the scope of m invention to the employment of flexural vi rations. 'The method which I have described can be used for maintaining oscillations in any mode of vibration of a crystal in circuits, which feed back energy from output to input through the crystal itself.

It can also be applied to plates cut in different orientations from the original crystal substance and plates cut from many different materials having piezo electric properties. p,

The mode of o eration of the systems which I have described and their relation to systems heretofore known can be somewhat better realized by reference to Figs. 3, 4 and 5 which show diagrammatically a piezo electric crystal with different arrangements of electrodes and related three electrode tube and simple circuits. In Fig. 3, the crystal is mounted with three electrodes, A, B, and C, of which B covers substantially all of one side ofthe crystal, while A and C cover restricted areas near the ends. A is connected to the plate, C to the grid, and B to the filament, of the three electrode electron tube. The input circuit of the tube includes electrode B and electrode C. The output circuit includeselectrode B and electrode A.-

Such a condit on is undesirable. for one reason, because unsymmetrical stresses set up strains which easily fracture the crystal.

In Fig. 4 is shown a crystal mounted with four; electrodes D, 'E, F and G, all of which cover restricted areas near the ends of their respective sides of the crystal. D cor;

{ and G are connected together, and to the filament. F and G performthe same function in the circuit as the single electrode B of Fig. 3 and the fact that electrode B has been split into the two electrodes F and G does not in any manner affect the operation of the circuit of Fig. 4, which will operate the same as has been described for Fig. 3,

and has the same disadvantages of unsymmetrical stresses.

In Fig. .5 is shown an underlying principle of the system of my invention, and its improvement over the arrangements heretofore used as shown in Figs. 3 and 4. .The crystal is provided with four electrodes, H, J, K-and L. H and K occupy restricted areas near the ends on the same side of the crystal, and J occupies a restricted area near the center of that side of the crystal. -L occupies substantially all of one side of the crystal, or may be split into smaller elec:

trodes; H and K are connected together and to the" plate of the tube; J is connected to the grid of the tube and L is connected to the filament of the tube. The arrangement of Fig. 5 is in general similar to that of Fig. 3 but the mounting of Fig. 5 provides for applying the fields in a symmetrical manner. It is obvious that the arrangement of Fig. 5 will apply to both ends of the crystal, the same strong exciting field due to the plate circuit and to the center of the crystal the comparatively weak field due to the grid circuit, and symmetrical stresses will be caused. If desired, these arrangements can be reversed, and the strong exciting field due to the plate of the tube applied at the middle of the crystal, and the weak field due to the grid applied at both ends, and symmetry still maintained. In similar manner the crystal mountings whichI have previously described in detail, shown in Figs. 1 and 2,

and which are suitable for exciting flexural vibrations, apply the electric field to the crystal in a symmetrical manner, and in this respect differ from the conventional mounting for fle'xural vibrations which has been heretofore'known.

I realize that many modifications of the crystal mounting and circuit arrangements of my invention are possible without departing from the spirit of my invention and it is to be understood that my invention shall not be limited by the foregoing specification or by the accompanying drawing but only as defined in the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. A mounting for a piezo electric element comprising in combination a plurality of electrodes spacially positioned immediately adjacent to opposite sides of said element at least three of said electrodes being positioned on the same side of said crystal element and two of said electrodes on said side which are not adjacent being conductively trodes being on the other side of said crystal and respectively positioned one near each end of said crystal and one near the middle of said crystal.

3. In piezo electric crystal apparatus, a iezo electric crystal, a plurality of electrodes 1n electrical relation with said crystal, at

least one of said electrodesbeing on one side.

of said crystal and three of said electrodes being on the otherside of said crystal and res ectively positioned one near each end of sai crystal and one near the middleof said crystal, and each of said three electrodes being less than one-third the length of said crystal.

4. In piezo electric crystal apparatus, a

piezo electric crystal, a plurality of elec-.

trodes in electrical relation with said crys-- tal, at least one of said electrodesbeing on one side of said crystal and at least three of said electrodes being on the other side of said crystal and respectively positioned one near each end of said crystal and one near the middle of said crystal, an electrical amplifying device, input and output circuits therefor, said input circuit being connected to said electrode on one side of said'crystal and to the middle electrode on the other side of said crystal, and said output circuit being connected to said electrode on one side of said crystal and to saidend electrodes on the other side of said crystal conductively connected together.

6. In piezo electric crystal apparatus, a piezo electric crystal, a ,plurality of electrodes in electrical relation with said crystal, at least one of said electrodes being on one side of said or stal and at least three of said electrodes being on the other side of said crystal'and respectively positioned one near each end of sa1d crystal and one near the middle of said crystal, an electrical amplifying device, input and output circuits therefor, said input circuit being connected to said one electrode or common electrode on one side of said crystal and to said end electrodes on the other side of said crystal conductively connected together, and said output circuit being connected to said one or common electrode on one side of said crystal and to the middle electrode onthe other side of said crystal. I

7. The method of applying to a piezo electric crystal two voltages of unequal magni-- tude which consists in applying one of said voltages between one side of said crystal and the middle of the o posite side of said crystal, and applying the other of said voltages between one side of said crystal and the two ends of the opposite side of said crystal.

8. The method of applying to a piezo electric crystal two voltages of unequal magnitude which consists in applying said voltages spacially symmetrically with reference to a median plane of said crystal which is perpendicular to the faces of said crysta to which said voltages are applied.

9. The method of applying to a piezo electric crystal a lurality of voltages of unequal magnitu e which consists in applyin said voltages spacially symmetrically, wit reference to a median plane of said crystal which is per endicular to the faces of. said crystal to which said voltages are applied.

10. In piezo electric crystal apparatus, a

iezo electric crystal, a pluralit of electrodes in electrical relation with sa1d crystal, at least one of said electrodes bein on one side of said crystal and at least t ree of said electrodes being on the other side of said crystal and respectively positioned one near each end of said crystal and one near the middle of said crystal, an electron tube having cathode, grid, and anode, an output circuit connecting said anode to said cathode,

said cathode connected to one electrode on one side of said crystal, said grid connected to the middle electrode on the opposite side of said crystal, and said anode connected to the end electrodes on the opposite side of said crystal conductively connected together.

11. In piezo electric crystal apparatus a iezo electric crystal, a plurality of electro es 1n electrical relation with said crystal, at least one of said electrodes being on one side of said crystal and at least three of said electrodes being on the other side of said crystal and respective] positioned one near each end of said crystal and one near themiddle of said crystal, an electron tube having cathode, grid and anode, an output circuit connecting said anode to said cathode, said cathode connected to one electrode on one side of said crystal, said grid connected to the end electrodes on the opposite side of said crystal conductively connected together, and said anode connected to the middle electrode on the opposite side of said crystal. j

12. In piezo electric crystal apparatus, a

iezo electric crystal, a pluralit of electrodes 1n electrical relation with sai crystal, said electrodes in conductive electrical relation on each side of said crystal bein disposed s mmetrically with reference to the median p ane of said crystal perpendicular to the face of said crystal to which said electrodes are applied and also r endicular to the direction along which sa1d e ectrodes are arranged.

13. In piezo electric crystal apparatus, a

iezo electric crystal, a plurality of electrodes in electrical relation withsaid crystal, at least one of said electrodes being on one side of said or stal and at least three of said electrodes eing on the other side of said crystal and respectively positioned one near each end of said crystal and one near the middle of said crystal, an electron tube having cathode, grid, shielding grid, and anode, an output circuit connecting said anode to'said cathode, said cathode connected to one electrode'on one side of said crysal, said grid connected to the'middle electrode on the opposite side of said crystal, and said anode connected to the end electrodes on the opposite side of said crystal conductively connected together.

14. In piezoelectric crystal apparatus a piezo electric crystal, a plurality of electro es in electrical relation with said crystal, at least one of said electrodes being on one side of said or stal and at least three of said elec: trodes eing on the other side of. said crystal and'respectlvely positioned one near each end of said crystal and one near the middle of said crystal, an electron tube having cathode,

grid,shielding grid, and anode, an output circ'uit connecting said anode to said cathode,

said cathode connected to one electrode on one side of said crystal, said grid connected to the end electrodes .on the opposite side of said crystal conductively connected together, and said anode connected to the middle electrode on the opposite side of said crystal.

15. In piezo electric crystal apparatus, a piezo electric crystal, a plurality of electrodes in electrical relation with said crystal, two of said electrodes disposed on one side of said crystal and substantially along the edges thereof and parallel to each other but not in electrical conductive relation with each other, another electrode disposed on the opposite side of said crystal and substantially along an edge-thereof and parallel to said first mentioned, electrodes, and three electrodes disposed along the other edge of said opposite side of said crystal and parallel'to said first mentioned electrodes, said last mentioned three electrodes being electrically structurally insulated from each other, one of said last mentioned three electrodes being positioned at about the middle of the edge of said crystal and the other two of said last mentioned electrodes being of substantially equal length and positioned substantially at the ends of said edge and being electrically connected together.

16. In piezo electric crystal apparatus, a piezo electric crystal, a plurality of electrodes in electrical relation with said crystal, two of said electrodes disposed on one side of said crystal and substantially along the edges thereof and parallel to each other but not in electrical conductive relation with each other, another electrode disposed on the opposite side of said crystal and substantially along an edge thereof and parallel to said first mentioned electrodes, and three electrodes disposed along the other edge of said opposite side of said' crystal, and parallel to said first mentioned electrodes, said last mentioned three electrodes being electrically structurally insulated from each other, one of said last mentioned three electrodes being positioned at about the middle of the edge of said crystal and the other two of said last mentioned electrodes being of substantially equal length and positioned substantially at the ends of said edge and being electrically connected together, an electron tube having cathode, grid and anode, an output circuit connected between said cathode and said anode, said anode being connected to the end electrodes of the group of three electrodes positioned on one ed e of said crystal and to the electrode on tli diagonally opposite said group of three electrodes, said grid connected to the middle electrode of said group of three electrodes, and said cathode connected to the electrodes on the two other edges of said crystal which are diagonally opposite each other, whereby stresses are symmetrically applied to said crystal.

17'. In piezo electric crystal apparatus, a piezo electric crystal, a plurality of electrodes in electrical relation with said crystal, two of said electrodes disposed on one side of said crystal and substantially along the edges thereof and parallel to each other but not in electrical conductive relation with each other, another electrode disposed on the opposite side of said crystal and substantially along an edge thereof and parallel to said first mentioned electrodes, and three electrodes disposed along the other edge of said opposite side of said crystal nd parallel to said first mentioned electro es, said last mentioned three electrodes being electrically structurally insulated from each other, one of said last mentioned three electrodes being positioned at about the middle of the edge of said crystal and the other two of said last mentioned electrodes being of substantially equal length and positioned substantially at the ends of said edge and being electrically connected together, anelectron tube having cathode, grid and anode, an output circuit connected between said cathode and said anode, said grid being connected to the end electrodes of the group of three electrodes e edge of the crystal positioned on one edge of said crystal, and

on the twoother edges of said crystal which are diagonally opposite each other, whereby stresses are symmetrically applied to said crystal.

18. In piezo electric crystal apparatus, a piezo electric crystal, a p urality of mu s of electrodes in electrical relation wit said crystal, the electrodes constituting each group being conductively connected together and said groups bein electrically insulated from each other, sai electrodes of each of said groups in conductive electrical relation being disposed symmetrically with reference to the median plane of said crystal pe ndicular to the face of said crystal to which said electrodes are aplied.

19. A piezo electrlc crystal unit comprising a pieza electric crystal and a plurality of electrodes in electrical relation with said or stal and positioned on opposite faces of said crystal, one of said electrodes being disposed on one face of said crystal, and three of the others of said electrodes being similarly disposed on an opposite face of said crystal, two of said three electrodes being conductively connected together, and the other of said three electrodes being positioned approximately at the center of said face.

In testimon whereof I afiix my signature.

AMISON R. HARRISON. 

